Scientists surprised to discover new butterflyfish

Because they are relatively well studied, scientists generally don’t expect to come across a new butterflyfish species. But that’s exactly what happened on an expedition by scientists with the San Francisco-based California Academy of Sciences when they were collecting live specimens 360 feet beneath the ocean’s surface in the Philippine’s Verde Island Passage.

Roa rumsfeldi was found on a mesophotic reef, which is a coral reef system that lies in a narrow band of the ocean known as the “twilight zone” — deep enough for sunlight to be scarce, but not pitch black like the deep sea. Mesophotic reefs are typically located somewhere between 200 and 500 feet beneath the ocean’s surface.

Scientists with the California Academy of Science’s Hope for Reefs initiative are trained to dive deep into the ocean’s twilight zone in order to explore the mostly unexamined coral reefs that lie there. They frequently collect live fish on their expeditions to these mesophotic reefs, and that is how they first came across Roa rumsfeldi.

There are well over 100 known species of butterflyfish, iconic coral reef dwellers that feature an array of distinctive and often colorful patterns.

Because they are relatively well studied, scientists generally don’t expect to come across a new butterflyfish species. But that’s exactly what happened on an expedition by scientists with the San Francisco-based California Academy of Sciences when they were collecting live specimens 360 feet beneath the ocean’s surface in the Philippine’s Verde Island Passage.

The discovery of an unknown butterflyfish was so unexpected, in fact, that Luiz Rocha, curator of ichthyology at the California Academy of Sciences and lead author of a study in the journal Zookeys describing the new species, says he and his team chose to name the fish after former U.S. Secretary of Defense Donald Rumsfeld and his infamous proclamation in 2002 about “known unknowns” and “unknown unknowns.”

“We named this reef fish Roa rumsfeldi because, as Donald Rumsfeld once said, some things are truly ‘unknown unknowns,’” Rocha said in a statement. “This fish caught us completely off-guard.”

Roa rumsfeldi was found on a mesophotic reef, which is a coral reef system that lies in a narrow band of the ocean known as the “twilight zone” — deep enough for sunlight to be scarce, but not pitch black like the deep sea. Mesophotic reefs are typically located somewhere between 200 and 500 feet beneath the ocean’s surface.

Scientists with the California Academy of Science’s Hope for Reefs initiative are trained to dive deep into the ocean’s twilight zone in order to explore the mostly unexamined coral reefs that lie there. They frequently collect live fish on their expeditions to these mesophotic reefs, and that is how they first came across Roa rumsfeldi.

“Our human bodies are not really compressible, but fish have swim bladders for buoyancy that can’t make the journey from twilight zone depths to the surface,” Bart Shepherd, director of the Steinhart Aquarium at the California Academy of Sciences and co-director of the Hope for Reefs initiative, said in a statement. “We gently moved this Roa to a special lightweight decompression chamber designed just for fish, brought it to the surface, and attentively cared for it through the flight back to San Francisco and into our aquarium.”

Even the scientists themselves didn’t know at first that they had come across a previously unknown species, however.

“After traveling from the deep reefs of the Philippines to our aquarium in San Francisco, former Academy aquarium biologist and co-author Matt Wandell noticed a black fin spine that looked different from other known Roa we’ve collected in the past,” Rocha, who is the other co-director of the Hope for Reefs initiative, said. “It was a light bulb moment for all of us.”

Like many other butterflyfish, the brown-and-white-striped Roa rumsfeldi has an eye-like spot on its flank, which likely helps confuse predators.

The discovery of R. rumsfeldi off the coast of the Philippines brings the total number of species in the genus Roa to five. Though closely related, the species are widely distributed across the Indian and Pacific Oceans: R. australis is found near Australia, R. excelsa near Hawaii, R. jayakari near India, and R. modesta near Japan.

Many of the live specimens brought back to California by the Academy’s scientists end up on display in the Steinhart Aquarium. Roa rumsfeldi, some of its closest relatives, and several more mesophotic marine species from around the world can currently be seen in an exhibit titled “Twilight Zone: Deep Reefs Revealed.”